Air classifier



H. HARDINGE AIR CLASSIFIER June 7, 1960 2 Sheets-Sheet 1 Filed July 13,1956 INVENTOR HAELOWE HIED/NEE ATTORNEY H. HARDINGE AIR CLASSIFIER June7, 1960 2 Sheets-Sheet 2 Filed July 13, 1956 INVENTOR 4 e4 ow:HAED/IVGA' ATTORNEY United States Patent tee I atented June 7, 1960 AIRCLASSIFIER Harlowe Hardinge, 2'40 Arch St., York, Pa. Filed July 13,1956, Ser. No. 597,756 A 3 Claims. (Cl. 209-144 This invention relatesto a process and apparatus for classifying pulverized material andparticularly for separating relatively coarse particles of material of apredetermined range of sizes from a fluid stream containing a mixture ofsaid particles with relatively finer sizes of material.

This application is a continuation-in-part of patent application SerialNo. 339,271, filed February 27, 1953, and now issued as Patent No.2,758,713,.dated August 14, 1956. Y

The process and apparatus comprising the present invention areespecially useful with grinding mills and particularly with grindingmills from which a fluid stream carrying entrained particles of solidmaterial of various sizes moves upwardly for transmission to aclassifying system such as comprises part of the present invention.However, it is to be understood that the invention is not to berestricted for use with grinding mills or machines of this type orhaving upwardly directed discharge means since the invention has otherapplications of use.

A problem frequently encountered in classifiers of the type to which thepresent invention pertains is that stratification and agglomerationofthe material occurs during the passage thereof through the apparatus.This is particularly so in classifiers wherein a fluid stream isestablished and utilized for purposes of moving the material through theclassifiers while entrained in said stream.

Various attempts have been made to reduce this tendency but theefficiency of most of these attempts has not been as great as desired.Further, many of the classifiers which have been developed in an attemptto solve this problem have been expensive to manufacture and operate,and also have been complicated.

The principal object of the present invention is to provide a processand apparatus for classifying pulverized material and, moreparticularly, for separating relatively coarse material from relativelyfine material entrained as a mixture in a fluid stream, the details ofthe process and the apparatus being such as to result in substantiallyno stratification and agglomeration of the particles as they passthrough the apparatus, the speed and directions of movement of thestream through the system being such as to eflect greater efliciency ofseparation and prevention or stratification than has been possibleheretofore.

More specifically, the process and apparatus comprising the presentinvention includes a system comprising a casing which communicatespreferably at the bottom with a suitable conduit. A fluid stream havingvarious sizes of particles of solid material entrained therein entersthe lower end of said casing through said conduit. An impeller isprovided in the casing which has means operable to produce a circularcomponent in the path of v the stream while the stream progressivelyrises, and conduits connected in the system and communicatingparticularly with the upper portion of said casing preferably have anegative pressure maintained therein so as to produce a desired movementof the fluid stream through said casing and conduits comprising thesystem.

' As the stream moves through said casing, the impeller also engagesparticularly the coarser particles and deflects them transverselyagainst the walls of the casing, whereupon these particles drop to asuitable collector for return to the mill or otherwise. The finerparticles remain entrained in the stream as the stream continues to moveupwardly through the casing and the simultaneous circular movement ofthe stream results in the path thereof being spirally upward,particularly as the stream exits from the upper part of the casing.

While the details of certain elements of this system and especially saidimpeller are described and claimed in aforementioned Patent No.2,758,713, dated August 14, 1956, the present application, althoughincluding drawings similar to those in said patent, pertains principallyto the apparatus and process by which the particle entrained fluidstream is caused to move not only through the casing which contains theimpeller but also through the exit conduit means of the system in ahighly efficient manner which minimizes stratification of solidparticles within the stream.

Further, the invention described and claimed herein concerns a processand apparatus which .combines dynamic movement with the force of adischarging, particle entrained, fluid stream to produce an eifectivecentrifugal force with minimum power loss, as well as increasingclassification efiiciency and the lowering of overall power comsumptionfor a. given efficiency as compared with existing classifiers.Correspondingly, the dynamic movement of the vaned impeller is continuedin its centrifugal movement by virtue of the nature of the outlet fromthe confined chamber being substantially in line with the direction ofmovement of the fluid stream as produced by said impeller.

Further, an important aspect of the improvement offered by the presentinvention comprises the abrupt changing in direction of the exhaustingfluid current, for example, from a substantially vertical direction to asubstantially horizontal direction, without appreciable loss in pressuredrop and while subjected to only minimum frictional lossesfdue tominimizing of eddy currents.

Still further, the inlet passage of the apparatus of the presentinvention is provided with a constriction so arranged as to produce aventuri effect, thereby increasing the movement of the particleentrained fluid stream through the system with all of its attendingbenefits.

thereby enhancing the separation of such finer fraction of particles inthe stream from the coarser particles.

Details of the process and one exemplary embodiment of apparatus capableof performing said process to produce the benefits "of the presentinvention are illustrated in the accompanying drawings comprising a partof the application and are described in the following specification.

In the drawings:

Fig. 1 is a vertical elevation, partly in section, of an exemplaryclassifying system including a classifying unit illustrated in greaterdetail in Figs. 3 and 4.

Fig. 2 is a diagrammatic top plan view of the system illustrated in Fig.1.

Fig. 3 is a side elevation, partly. in section, illustratin'gprincipally an exemplary embodiment of classifying unit incorporated inthe classifying system illustrated in Figs. 1 and 2.

Fig. 4 is a fragmentary, diagrammatic plan view of the upper portion of*t heunit illustrated in Fig. 3. I,

The process comprising the present invention may be performed in anumber of different types of apparatus, one exemplary embodiment ofwhich is illustrated in Figs. 1 through 4. V V 7 Referring to Fig. 1, aclassifying system is shown which includes one embodiment of classifyingunit 10 comprising a casing 12 which preferably is generallyfrusto-conical in shape, the axis of the casing extending substantiallyvertically. The lower end portion of the casing 12 is shown connected toa collector 14 which receives coarser particles separated from a fluidstream in which said particles were entrained as will be described indetail hereinafter.

Extending upward through the collector 14 is an inlet or entrance end 16of a conduit which extends preferably axially of the casing 12. The topof the casing 12 is closed by cover 18 through which an exhaust conduit2G extends substantially vertically and preferably in axial alignmentwith the casing 12. A shaft 22 extends into the conduit 20 and isrotatably supported by suitable bearings 24 fixed relative to theconduit 20. A motor 26, which is preferably of the variable speed type,is fixedly supported relative to the conduit 20 and a belt 23 connectssuitable pulleys on the motor 26 and shaft 22 as clearly shown in Fig.3, whereby the motor positively drives the shaft 22.

An agitator or impeller 30 is fixed to the lower end of shaft 22 and isrotated thereby dynamically to cause the stream to assume a curved pathwhile rising, resulting in the particles in the stream being subjectedto centrifugal force while the stream 'moves spirally upward due also tonegative pressure in unit 10, to be described hereinafter.

Referring particularly to Fig. 3, it will be seen that the impeller 30comprises a pair of plate-like members 32 and 34 which extendtransversely to and are also fixed to the shaft 22 in longitudinallyspaced relationship to each other. A plurality of elongated vanes 36extend between and are secured to the plate-like members 32 and 34, saidvanes preferably being spaced peripherally even distances around saidmembers and the outer edges of the vanes 36 are also preferably disposedat an acute angle to the side walls of the casing 12, as clearly shownin Figs. 1 and 3. This is made possible by the member 34 having asubstantially larger diameter than mernber 32.

The impeller will function to achieve desirable results, in accordancewith the present invention, which are described in detail hereinafterwhen only the members 32 and 34 and vanes 36 are fixed thereto. However,the efliciency of the apparatus, and correspondingly of the process,usually is increasedby providing shield means 38 which preferably is acone of suitable material such as sheet metal and extends between themembers 32 and 34 as well as between the vanes 36 adjacent the inneredges thereof to enhance the teetering effect referred to above whensuch condition is desired and advantageous. This arrangement produces awell defined annular, frusto-conical space or passage 40 between thecasing 12 and the impeller 30, said space having the diameter thereofprogressively expand from bottom to top. Also, the angle of thefrusto-conical shield means 38 is greater than that of casing 12 and thedifference in these angles preferably. is such that, as the space 40increases in diameter, it decreases in Width, or thickness, whereby apassage. of substantially constant cross-sectional area andsubstantially uniform velocity is provided. This arrangement allows thecoarser particles which may enter this zone to drop down against arising .fluid column without encounteringan increase in average velocityas would result if the area of the zone was reduced materially at thelower portion of passage 40.

Extending tangentially from and communicating with the outlet conduit 20is another conduit 42 and the upper end of the conduit 20 is closed by acover or plate 44 which may be coextensive with the upper wall of theconduit 42 as shown in Fig. l.

While a classifier unit of the type described above and illustrated inFigs. 1 and 2 is useful to perform various kinds of classifyingoperations, it is particularly useful in a pul'verizi'n'g andclassifying system, one exemplary illustration of such system beingshown in Figs. 1 and 2, wherein the classifier unit 10 is illustrated insectional view. Said system may housed in conjunction with a mill, notillustrated, if desired, the mill for example being disposed below theconduit outlet end 16. In any event, it is contemplated that material tobe classified is in the form of a fluid stream in which a relativelywide range of particles of pulverized material is entrained and saidstream is introduced through entrance 46 to the system.

As illustrated in Fig. 1, said entrance has a balanced air-lock 48operatively positioned so as to controlthe inlet of material to thelower portion of uptake conduit 50. Said air-lock 48 is adjustable bymeans of a movable weight 49 or the like so as to control desirably theinlet of air as well as material to be classified. Somewhat of a chokefeed thereby is afforded to permit a desired amount of vacuum to bemaintained in the unit 10 and the take-off therefrom. v

The system also includes a blower 52 which discharges in a direction toflow upwardly through the conduit 50 and thereby carry the fluid streamin which the pulverized material is entrained to the classifier 10. Ithas been found in actual practice that, depending of course upon theforce of the exhaust of the blower 52, the fluid stream discharging fromconduit 50 into the classifier 10 is capable of carrying particles ofrelatively large size to the classifier 10. A wide range of smallersizes of particles are also entrained in said stream moving to theclassifier.

Further, it will be noted the inlet chute 46 permits the enteringmaterial to fall by gravity but as the material enters uptake conduit50, its path is immediately reversed and it is carried upward by theup-draft in conduit 50 which engages the entering material head-on. Thisresults in a minimum amount of stratification of solid particles withinthe stream of material moving to the unit 10. Such reversal of directionof the entering material also is greatly enhanced and the buoyingcapacity of the fluid stream in conduit 50 is increased greatly overnormal values by providing constricting means 51 in the lower end ofconduit 50 to produce a venturi effect; i.e., an increase in velocityand drop in pressure.

Referring particularly to Fig. 3, it will be seen that the fluid stream54 of entrained particles enters the casing 12 in a substantiallyvertical path at considerable speed and impinges against the lowersurface of the platelike member 32 which is preferably planar andimperforate and transverse to the path'of the stream. At least thecoarsest of the particles within the stream will be deflectedtransversely and will be impinged against the sidewalls of the casing 12as indicated, for example, by the broken line arrows 56. The rotation ofmember 32 enhances this function. Said separated coarser particles willhit the sides of the casing 12 and fall by gravity down said sides intothe collector 14. The material collected in collector 14 is dischargedthrough the oversize spout and airlock 58.

The stream of material from which some of the coarser particles havethus been removed then moves upward through the space 40 which isdefined by the casing 12 and the impeller 30,. Said impeller will berotated at ,a speed suitable to achieve greatest eliiciency dun'ng thegas es classifying operation. This impeller produces dynamic movement ofthe stream which combines with the upward movement to produce aneffective centrifugal force that increases classification efi'iciencywith a minimum overall power consumption for a given efiiciency. Thedynamically moved vanes 36 of the impeller also will engage otherrelatively coarse particles within the stream moving generally upwardthrough the space 40 and will cause them to be thrown or impingedagainst the sides of the casing 12 and from there said particles Willmove into the collector 1 4 by gravity.

It will be noted that the passage 40 is relatively long and the vanes 36also act continually to disturb and break up any tendency for unbalancedloading of one portion of the classifier as opposed to another, wherebythe air velocities are more evenly distributed than is otherwisepossible and the air loadings are maintained substantially constant whenair is used as the fluid medium. In addition, the buoying effect of the.air and the centrifugal force caused by the rotating member 30 ismaintained substantially constant with the result that the coarserparticles which are thrown out of the stream by the vanes of theimpeller are kept substantially clean of the fines which would otherwisetend to be entrained with them in an unbalanced load. Thus, the coarseparticles in settling and moving downward into the collector 14- containa very minimum of fines. Further, such centrifugal movement of the fluidstream in a confined chamber aids the dynamic movement of the vanedimpeller.

The fines, together with the finer particles of oversize, travel upwardbetween the vanes 36 and through the space 46 as the stream rises towardthe outlet conduit Zil. The diverging effect of the vanes 36 causes anincrease in the velocity of the stream and the centrifugal forceproduced by the impeller 30 produces further refinements andclassification of the particles in this portion of the apparatus withoutthe heavy loading of coarser particles which have been removed from thestream before the material reaches the upper zone thereof.

Vanes 36 also produce a winnowing action which is described in detailand claimed in said aforementioned patent. Such action causes the streamto assume a somewhat wavering but generally upward path indicated by thesolid arrow lines 60, said stream containing the fines intermingled withrelatively medium particles of oversize. Some of the latter are causedto be thrown from the stream by vanes 36 so as to impinge against thewalls of the casing 12 as indicated by the broken line arrows 62. Theseparticles move down the walls of the casing 12 by gravity as indicatedby other broken line arrows 62. Some of the medium oversize particlesare carried to the upper zone 64, where they drop to plate 34 and aredischarged by centrifugal force or blade 68, to slide down wall 12 todischarge spout 58. The vanes 36, in conjunction with the deflectingaction of member 32, cause the stream first to move toward the sidewalls of the casing 12 and said stream then is waveringly deflectedinward toward the impeller 30 which causes engagement of the mediumoversize particles in said stream with the vanes 36. The centrifugalforce of the impeller will also cause diversion of the stream assubsequently deflected back toward the impeller preferably a pluralityof times as indicated by the arrows 60 and resulting in a combinedwinnowing and deflecting effect upon the stream passing through thespace 40.

As has been stated hereinabove, the operation of this type of classifieris relatively eflicient even when the shield means 38 is omitted.However, a more eflicient cleaning of the oversize particles results ifthe shield 38 is embodied in the impeller 30. Saidshield also moreprecisely defines the annular space or passage 40 which tends todecrease the consumption of power and wear 'on parts in this zone byeliminating a space where turbulence is caused but which performs littleor no useful purpose; i

As referred to in the aforementioned patent, this classifier willfunction however without shield 38 being included in the impeller 30 andthe above described wavering function will take place when said shieldis omitted. However, the teetering eifect will not occur when the shield38 is omitted and in operations under certain conditions, such teeteringis not necessary or advantageous as for example, where the cleaning ofso-called intermediate sizes is not necessarily advantageous and suchomission of the shield will eliminate the attendant cost thereof fromthe total cost of the apparatus. a

It has also been found that, generally, if the perimeters of the members32 and 34 extend'somewha-t beyond the shield 38, as shown in Fig. 3, thepassage of the fluid stream between the edges or perimeters of saidmembers and the casing 12 is restricted to a greater degree than therestriction between shield 38 and casing 12. Thus, the velocity of thestream past the perimeters of the plate-like members 32 and 34 isincreased and such increase in velocity also enhances the winnowing andhindered-settling action of the particles within the stream as comparedwith the operation of a construction in which said members 32 and 34 donot extend beyond the shield 33.

From Fig. 3 particularly, it will be seen that the upper member 34 isspaced a substantial distance from the cover 18 of casing 12, as well asoutlet conduit 20. In view particularly of the conical configuration ofcasing 12, anenlarged zone 64 is provided in the upper portion of casing12. The upper ends of the vanes 36 preferably extend upwardly beyond themember 34 a substantial distance into the zone 64. Further, in thepreferred embodiment of the invention, the lower end of outlet conduit20'projects into zone 64 so that the fluid stream containing entrainedfines which are to be removed through conduit 20 travels upward intozone 64 as shown by the arrows 60. The currents designated by arrows 60tend generally also to curve toward the upper surface of the member 34with the result that the relatively medium particles therein are thrownagainst the upper surface of member 34.

This deposit of coarser particles may be discharged from the member 34by centrifugal force induced by the rotation of the' impeller 30 if thespeed thereof is sufficient for such purposes. However, under somecircumstances, depending on the loading of the stream and the speed atwhich said stream is introduced to the classifier, the rotational speedof the impeller 30 may be such that insufficient centrifugal force isdeveloped to produce the desired amount of discharge of the coarserparticles from. member 34. To insure substantially complete removal ofsaid coarser particles from member 34, scraper 68 is supported adjacentsaid upper surface, for example, by a bracket 70 fixed to conduit 20.Said scraper is preferably positioned at a suitable angle within a planeparallel to member 34 so as to insure scrapping and discharge of thecoarser particles from the upper surface of member 34 and cause the sameto fall against the walls of the casing 12 and slide down the same intothe collector 14.

While it is diflicult to determine exactly what takes place in theenlarged zone 64 of the classifier, tests in transparent models tendgenerally to indicate that two forces seem to be exerted upon the streamin said zone. One of these is the force of the stream passing throughthe classifier from the entrance conduit 16 to the outlet conduit 20 andthe other force is centrifugal and created by the rotation of the vanes36. The result appears to be an inward and downward thrust of'the streamwith the finer particles entrained therein that have not previouslysettled. In this zone, a sharp degree of classification appears to takeplace due to the diiference in the inertia of the particles within thestream. The coarser particles tend to go to the point where there isless agitation arid this is near the top of member- 34. At or just abovethe rotating member 34, the agitation seems to be greatly reduced and areversal of direction close to member 34 occurs with the result that-thecoarser particles remaining in the stream drop out and are eitherdeposited or are thrown by centrifugal force from the member 34 asdescribed above. These particles move through the vanes .36 and fall tothe walls of the casing 12, down which they slide to the collector 14 asdescribed hereinabove.

The fluid stream from which the coarser particles have been removed andin which fines are still entrained, flows upward through outlet conduit20 and into take-E conduit 42. Impeller 30 introduces-a rotationalcomponent of movement into the upwardly moving, spiralling stream andsaid rotation is in such a direction as naturally to enter the take-offconduit 42 which extends tangentially from the side of conduit 20 thatnaturally would receive the rotating stream in the same line of travel,as clearly shown in Figs. 2 and 4. This arrangement results inminimizing stray or eddy currents with reduction in any pressure drop atthe outlet or exhaust end of the classifier and also minimizesfrictional losses, thus resulting in de creased wear and powerconsumption in this portion of the system. Further, less head room isrequired by such tangential take-ofi as compared with conventionalsystems of this nature and avery effective and simple mounting for theimpeller and drive means therefor also made possible.

Take-off conduit 42 is illustrated in Fig. 1 as conducting the stream offines into a separator 72 which separates the fine product from thefluid, such as air, in a manner well known in the art. The fine productis then recovered through a suitable air lock 74. The air thus freed ofthe fine product is returned to the blower or fan 52 through conduit 76.Thus, the blower 52, being in communication with conduit 76, separator72, and conduit 42, places a suction upon the outlet conduit 20 andthereby facilitates movement of the fluid stream from the classifierinto the outlet conduit 20. Flow of air through the system illustratedin Figs. 3 and 4 is also controllable by damper 78 in a well knownmanner in systems of this nature. Back pressure produced by the damper78 is sufficient to create a negative pressure on the other side of thedamper 78, thus putting the system under a partial vacuum as is wellknown in the art. Any leakage entering the system through the variousair locks or otherwise is vented through a suitable pipe 80, whichventing is controlled by damper 82 at the only point in the system underpressure.

While no specific means other than a variable speed motor have beendescribed herein for varying the speed of the impeller, it will beunderstood that any one of a number of other standard expedients may beutilized such for example as expansible V-pulleys or a variable gear boxbetween the motor and drive shaft of the impeller.

By including a power driven impeller with the classifier,

' it is found that power consumption is less than in commonly usedclassifiers wherein air is passed through the classifier by suitableblower means only for example, and the force of the air itself isrequired to cause any centrifugal or other action to throw out theoversize particles. Thus, in the herein described classifiers as well asa system embodying the same, there is less wear on the apparatus unit,conduits and the system generally due to the fact that the streamcontaining entrained particles may be moved through the system at alower rate of speed than is required in the above described classifiersWhichhave no rotating impellers.

While the specific merits and advantages of the details of the impellerand its relation to casing 12, as well as the wavering and winnowingeffects produced thereby, are advantageous to the classifying systemdescribed and claimed herein, these details are claimed in theaforementioned patent. The principal novel features of the inventiondescribed and claimed herein comprise the process and system by which aparticle-laden fluid stream is moved steadily and progressively along apath and during a portion of such path, the stream dynamically is causedto move spirally to facilitate the development of centrifugal forces toseparate certain coarser particles from the stream while notsubstantially impeding the continued movement of the stream. Then, whenthe stream leaves the spiral portion of its path, it is caused to changedirection abruptly from upward to horizontal, for example, but due tothe take-off conduit 42 being tangential to the substantially verticaloutlet conduit 20, no appreciable loss by friction or drop in pressureis caused. This arrangement also results in minimum head room beingrequired to install the classifier unit of the system.

The exemplary illustration of one embodiment of apparatus'suited toperform the process referred to is well suited to being constructed,installed, and operated economically and also comprises part of theinvention. Other structures, however, are capable of performing theprocess described and claimed herein.

While the invention has been shown and illustrated in its preferredembodiments, and has included certain details, it should be understoodthat the invention is not to be limited to the precise details hereinillustrated and described since the same may be carried out in otherways falling within the scope of the invention as claimed.

I claim:

1. A classifier system for separating particles from one common fluidstream containing the same and comprising in combination, an upwardlyand outwardly tapering casing having an entrance adjacent the lower endthereof and arranged to introduce said fluid stream substantiallyaxially through said entrance into said casing, the upper end of saidcasing having an axially extending outlet for said' stream, an impellerextending axially within said casing for substantially the major portionof the length thereof and rotatable about the axis of said casing andoperable to cause said axially moving stream also to move spirally andoutwardly as it continues to move axially through said casing, vanes onsaid impeller extending upwardly from the lower end thereof to inducespiralling of said stream, and a conduit extending substantiallytransversely to the axis of said casing and tangentially connected toand intersecting the outlet at the upper end of said casing in adirection corresponding to the spiral motion of said stream as it entersand exits from said outlet, whereby said spiral movement imparted tosaid stream serves to change the discharge direction of said stream fromaxial movement through said casing to movement susbtantially transversethereto with a minimum of pressure drop and frictional losses.

2. A classifier system for separating relatively coarse particles from asingle continuous fluid stream containing intermixed relatively coarseand fine particles and comprising in combination, a casing extendingsubstantially vertically and having an entrance at its lower endarranged to receive all of said fluid stream of mixed particles, asubstantially cylindrical outlet conduit projecting axially from the.upper 'end of said casing, said stream being movable substantiallylongitudinally upward through said casing, a drive shaft extendingaxially through said outlet conduit and depending into said casing,impeller means within said casing extending longitudinally thereof atupwardly and outwardly diverging angles and connected to said driveshaft for rotation thereby Within said casing about the axis of saidshaft in spaced relationship to said casing, vanes on said impellerextending upwardly from the lower end thereof to induce spiralling ofsaid stream, said impeller means when rotated serving to deflect thecoarser particles from said stream against the walls of said casing andcausing said stream to assume a substantially spiral path as itprogresses in its entirety upwardly to said outlet conduit, meansarranged to receive said coarser particles deflected from said stream,closure means for the outer end of said outlet conduit, and a take-offconduit for the exiting fluid stream tangentially intersecting saidoutlet conduit in a direction corresponding to the spiral direction ofsaid stream induced by said impeller means, whereby pressure drop atsaid outlet is minimized.

3. A classifier system for separating particles from a fluid streamcontaining the same and comprising in combination, a substantiallyconical casing flaring upwardly and having an entrance adjacent thelower end thereof and arranged to introduce a fluid stream substantiallyaxially into said casing, the upper end of said casing having an axiallyextending outlet for said stream, an impeller within said casing havinga conical wall flaring upwardly at a Wider angle than said casing andspaced inwardly therefrom to provide a conical passage between saidcasing and impeller wall having a substantially constant cross-sectionalarea, said impeller being rotatable about the axis of said casing andoperable to cause said axially moving stream also to move spirally as itcontinues to move axially through said conical passage of said casing,and a conduit extending substantially transversely to the axis of saidcasing and tangentially connected to and intersecting the outlet of saidcasing in a direction corresponding to the spiral motion of said streamas it enters and exits from said outlet, whereby said spiral movementimparted to said stream serves to change the discharge direction of saidstream from axial movement through said casing to movement substantiallytransverse thereto with a minimum of pressure drop and frictionallosses.

References Cited in the file of this patent UNITED STATES PATENTS1,367,636 Sturtevant Feb. 8, 1921 1,367,637 Sturtevant Feb. 8, 19212,153,270 Osgood Apr. 4, 1939 2,422,203 McNeill June 17, 1947 FOREIGNPATENTS 639,537 Germany Dec. 7, 1936

